What is Units: Definition and 996 Discussions

English units are the units of measurement used in England up to 1826 (when they were replaced by Imperial units), which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.
The two main sets of English units were the Winchester Units, used from 1495 to 1587, as affirmed by King Henry VII, and the Exchequer Standards, in use from 1588 to 1825, as defined by Queen Elizabeth I.The English units were replaced by Imperial Units in 1824 (effective 1 January 1826) by a Weights and Measures Act, which retained many though not all of the unit names and redefined (standardised) many of the definitions.
Use of the term "English units" can be ambiguous, as, in addition to the meaning used in this article, it is sometimes used to refer to United States customary units, which have somewhat different definitions, or to Imperial units, the standard units throughout the British Empire and Commonwealth.

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  1. B

    Atomic Mass Units: Discrepancy Explained?

    Been many years since I took general and org chem and am currently reading general chem textbook as refresher. Came across defintion of amu (atomic mass unit). Text says that the mass of the carbon-12 atom is defined to be exactly 12 amu. However, a couple of pages over, I read that the mass of...
  2. F

    Units Converter - Free & Easy | Kamlex

    Nice free units converter http://www.kamlex.com/index.php?option=com_content&task=view&id=12&Itemid=28
  3. T

    What is the normalization of photon states in QFT?

    If you inspect the QED lagrangian, you'll find that the electromagnetic vector potential must have the units of [1] energy. According to Peskin and Schroder's QFT text, the expansion of the electromagnetic field operator is...
  4. S

    Solving a Carnot Engine Problem: What Unit Do I Use?

    I solved the problem, but I can't get the right unit for the answer. A Carnot engine whose low-temperature reservoir is at 16°C has an efficiency of 31%. By how much should the temperature of the high-temperature reservoir be increased to increase the efficiency to 70%? My numerical answer...
  5. S

    MeV to Joules Units : How? 'In Electricity'

    So Hi, how you transfer from MeV to Joules? Thx, Exam this Friday :)
  6. M

    From mol kg-1 atm-1 to Pa units

    Hello, as you see I'm trying to translate Henry's coeff. from mol kg-1 atm-1 to Pascals. Did anybody try it?? thanks, merely
  7. R

    Convert English & Metric Units: 200 cubic yards to cubic cm

    Metric unit conversions - 100 square kilometers to square centimeters Wouldn't the answer be 10000000? English units to metric units - 200 cubic yards to cubic centimeters How would I solve that? And does anybody know how I would enter my answers in the correct Unit Multiplier...
  8. L

    Units for Period of Pendulum Formula

    I found the formula for the period of a pendulum: --- T = 2∏√( L / g) T: Time L: Length of Pendulum g: Gravitational Force --- However, I couldn't find information about the units! If somebody could provide me with information regarding this, it'd be greatly appreciated. Thanks :cool:
  9. S

    Questions about classsical physics units.

    I've been reading a book called Physics Demystified. I'am currently on part 1 Classical physics, chapter 6 units and constants. I have some questions about some defftions and units: The meter: It says that the meter is defined by the distance of light travels through a perfect vacuum in...
  10. J

    Units from Operations: 1-kg/s^2, 2-m^3/s, 3-m^2, 4-coul^2/s

    Express in the simplest form the units resulting from the following. (1) [kg/m^2][m^2/sec], (2) [m^3/kg][kg^2/sec], (3) [m^5/sec^2] / [m^3/sec^3], (4) [(kg^2 x coul^2)/(sec^3)] / [(coul x kg)/(sec^2)]
  11. J

    What are the fundamental units of nature?

    So far, all i can think of is: mass, time, length & charge (maybe?). Temperature isn't even a fundamental unit, since it is a measure of kinetic energy of a particle (1/2*m*vrms^2=3/2*k*T, i think that's right...), am i missing any? If that's all of them, then that's pretty amazing to me.
  12. U

    Gradient Units: For Hooke's Law Graphs

    now, this is a rather basic question, but, i can't seem to find the answer... so anyhow, i always thought that a gradient diddent need units and was just used to compare the change between two things, but i think i may be wrong. so, if you are plotting extension (m) over force (n) for a...
  13. Astronuc

    Units, Conversions and some useful materials data

    http://www.simetric.co.uk/ " Info on SI Units " SI Unit Descriptions " SI Derived Units " SI Prefixes (mega, giga) " Imperial/UK Units " Scientific Notation --(i.e. what is 1.00E+09) " Metric Forum " Feet to metres calculator " Metres to feet calculator " British Thermal Units...
  14. topsquark

    English System Units and R value

    A quick units question. Serway gives the R value (for insulation) in English system units as: \frac{ft^2 \, ^o F \, h}{BTU} What unit does "h" represent? Thanks! -Dan
  15. S

    Validity of comparing units.

    What is time ? My maths is so rusty its almost non existant. I'm looking at the energy to mass equivalence formula and trying to work out an equivalent 'unit of time'. With my poor maths I get; e=mc^2e^(1/2)=m^(1/2)* c [In terms of units] e^(1/2)=m^(1/2)* (d/t)e^(1/2)*t=m^(1/2)* dt= d *...
  16. P

    What objects, in General Relativity, carry units?

    Hi, maybe someone could answer this for me, or at least confirm my answer. (It's not homework.) What objects, in General Relativity, carry units? My thinking is that coordinates, x^i, on manifold patches have no units. And the parameter, t, for a path x^i(t) has no units. So velocities with...
  17. A

    Magnetic Flux: Exploring What it Means and Its Units

    I started reading Lectures on Electrical Engineering Vol I, Steinmetz. I thought I should be able to understand most of it, but I don't get the first page! It says that: 'The total number of lines of force issuing from a magnet pole is called its magnetic flux. The magnetic flux, phi, of a...
  18. O

    Measurement units and complex numbers.

    I am programming a module used to convert measurement units. This will be part of a system that supports complex numbers. I never use complex numbers in my field but of course engineers and physicists do so I thought I should ask a couple of questions first. Q1. Is there anything unusual about...
  19. D

    What Are the Units of Electromagnetic Wave B?

    B = k / w ( Z x E) Check this equation by deriving the units for B w = omega Z = z hat
  20. P

    Different speeds of light w/ Planck Units

    OK so my whining for help covers writing a paper about how things would be different if the speed of light was changed to 65 mph. Right after getting the assignment I started thinking about dilations and all that. Then, I remembered Planck's constant. Light would still have to have the same...
  21. E

    What are the units of a wave function

    My intuition is that it would be unitless. But if it's magnitude squared is a probability density, then its units would have to be 1 over some power of length. Specifically 1/L^(n/2) where n is the dimension. Where's the error in my thought? Thanks
  22. S

    When should I be converting to units?

    I am new to the forum, and I am sure it will be evident by this first question, but I hope to learn a lot here. so.. here is what I was thinking about that prompted me to look for a math forum. Say I have (20cm)2. That would be 400 square centimeters, or, 4 square meters? Now, what if I...
  23. A

    Can Rev/s and Hz Represent the Same Frequency Measurement?

    for the frequency of revolution of electrons, the unit is expressed as rev/s but for the frequency of a photon, the unit is hz my question: can rev/s also equal hz?
  24. Astronuc

    Units and Conversion Factors

    A nice tutorial by E.J. ROSCHKE PROPULSION DIVISION JET PROPULSION LABORATORY, Caltech. http://www.its.caltech.edu/~culick/Roschke.pdf
  25. P

    Exploring Planck Units: Why Newton's Constant?

    I have been reading http://en.wikipedia.org/wiki/Planck_units Why do they use Newton's universal gravitational constant, when that is a low gravity approximation and general relativity is what it used to work things out?
  26. U

    Spectral Radiance and it's Units

    I'm told the spectral radiance of a source is in the following units W ---------------- cm^2 * sr * nm And I try to use this to figure the spectral output of monochromator (in W), but I can't seem to cancel out the units. I multiply the spectral radiance by four other terms...
  27. A

    Converting Electron Mass from kg to MeV/c^2: A Quick Guide

    how do you change the measurement unit for an electron mass from kg to MeV/c^2?
  28. 1

    Finding Units of Z[x]: Multiplicative Inverses or Identity?

    Hi, I have to find the units of Z[x]. I am little unclear and my book does not go into detail. Does U(Z[x]) mean I need to find every polynomial with integer cooefficients that has a multiplicative inverse? or do I have to find the multiplicative identity? I was thinking about both cases and...
  29. P

    Units of Gradient for s x s vs m

    If we plot velocity in ms-1 over time in seconds, the gradient of the curve is acceleration or ms-2. If we plot time squared i.e. s x s over distance in metres, what are the units of the gradient? :redface:
  30. S

    Units of F[x] in a Field F

    If F is a field obtain all the units in F[x]?
  31. H

    Calculating Proton-Proton Distance in CaSO4.2H2O with CGS-Units

    I'm having great difficulties with CGS-units. In an experiment involving NMR I have to calculate the proton-proton distance in CaSO4.2H2O. I have done the measurements and they are, I think, pretty good however I have some problems with the calculations because of the units. The formula I...
  32. F

    Comp Sci Converting Temperature Units with C++

    I know I am not a moron but this C++ is killing me, I have to write a program using functions to convert temp between c, f, k I am hung up // Mod4project2tempconvert.cpp : Defines the entry point for the console application. #include <iostream> using namespace std; double ftemp (double...
  33. M

    English vs. SI units of mass and weight

    Hi, We know that the SI unit for mass is the kg, and that for force is the Newton, where 1 N = 1 Kg x the acceleration due to gravity. On the other hand, the English unit for mass is the slug, and that for force is the pound, and again we have a similar relationship based on Newton's...
  34. S

    Is Magnetic Susceptibility Dependent on Units?

    i think magnetic susceptibility xm=M/H is contant and independent of the units we are working with. in different refferences, they sometimes quote mks or cgs units which gives different value of Xm. It confuses me. Is Xm units dependent? for example Xm for oxygen is about 10^-4 in cgs...
  35. C

    Units in a quantum barrier problem

    I have a quesion regarding a quantum physics assignemnt, I wonder what units I should use when calculating the transmission coefficient of a quantum barrier problem. I have got the following expression: T = \frac{4(E+V_0)}{(2E+V_0)cos^2a\sqrt{\frac{2m}{\hbar^2}(E-V_0)} +...
  36. N

    How do I Calculate Derived Dimensions from Fundamental Units?

    I need to work out to dimensions that are derived from their fundamental units... I am having a small amount of trouble working out exactly how to do this... eg: Force Pressure Energy (using W.D.= force x distance) Thankyou for your time.
  37. T

    The Connection Between Planck Units and the Uncertainty Principle

    I know that Planck Time is the amount of time it takes light to cross Planck Length, but how did they figure out Planck Length? What are all the Planck units, how large are they, and how were they figured out?
  38. F

    System of Base Units without Time

    can you imagine a system of base units* in which time was not included? *the system of base units is the following: quantity----------------------------name-----------symbol time--------------------------------second----------s length------------------------------meter------------m...
  39. L

    Converting Units: Apple and Cranberry Barrels, Cloud Water Volume and Mass

    I realize these may be easy to some of you, but I'm have a few issues. For the first one: Two type of "barrel" units were in use in the 1920s in the United States. The apple barrel had a legally set volume of 7056 cubic inches. The cranberry barrel, 5826 inches. If a merchant sells 50...
  40. S

    How to Calculate Time and Uncertainty for Rotating Pulsars

    Hello, perhaps you could help with a problem. Suppose a pulsar rotates once every 1.400 806 448 872 75 + or - 5 ms, where the trailing + or - 5 indicates the uncertainty in the last decimal place (it does not mean + or - 5ms). a. How many times does the pulsar rotate in 30.0 days? I...
  41. Y

    Atomic Physics: Representing Quantities without Units

    Can someone help me with representing some quantities without units. I found that in atomic physics atomic units usually aren't used. For example Energy is E=\frac{-1}{n^2} Period of classical electron orbital i given by T=2 \pi n^3 Here n is Principial quantum number. How are derived these...
  42. A

    How is that homogenous with respect to units?

    how is that homogenous with respect to units? i can't get it!
  43. A

    Conversion of electromagnetic units

    I would like to ask a question that I am having a hard time finding the answer to. This is my question: 1 volt per second equals 1 tesla per square meter equals 1000000000 nanotesla and yielding frequency of 42580000hz or 42.58mhz denotable through the proton precision frequency calculation...
  44. P

    Using cgs units, can I set c=h-bar=1?

    Using cgs units, can I set c = h-bar =1 ? or should I change some other units to do that? Thanks
  45. E

    Finding the quantity of a radioactive substance and standard units

    When finding the quantity of a radioactive substance remaining after a half life of time t, using the formula, T1/2=.693/lambda. do u have to convert the time to standard units, the second, if it is in mins, or yrs or days or months watever?
  46. S

    Conical Pendulum units problem

    Hello all , I encouter a problem solving this one : We are given a conical pendulum with : V - tan. speed of particle m - mass of rotating particle g - gravity acceleration...
  47. E

    Convert Km/h to m/s - No Conversion Factor Needed

    Hello. I am making a physics calculator, and I have to make a conversion Unit for the program. I need to know this (as an example) I need to convert Kilometers per hour to Meters per second. But no the usual way. I know that the conversion factor is 0.278 but I need to convert the...
  48. N

    Why Do Journals Use Inconsistent Magnetic Units?

    What is with magnetic units used in published papers? You can only compare ~1% of the published results. Some of the units I've seen emu, emu/g, Arb, a few don't even give units. How do these papers make it through the review process?
  49. P

    Solving a Physics Problem: Finding the Right Units

    i just need help with finding the units to a physics problem at the end. some examples... \sqrt{\frac{940N/m}{0.038kg}}*(0.25m) it comes out to 39m/s. i know that since it's velocity, it should always be m/s. but there are some question that i don't really know what the final units...
  50. marcus

    Can we transpose the Cambridge Handbook into natural units?

    I am interested in a system of natural units that I see used more and more frequently in Quantum Gravity research papers so I like to try using them. the units are like conventional Planck except |8piG| = 1 I want to see if there is anything in the Cambridge Handbook of Physics Formulas...
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